CN114221320A - Integrated arc extinction method for single-phase earth fault of interconnected power distribution network - Google Patents
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Abstract
The invention relates to an integrated arc extinction method for single-phase earth faults of an interconnected power distribution network, and provides flexible interconnection equipment with fully controllable zero-axis components, wherein the zero-axis components of all grid-connected ports of the flexible interconnection equipment are controlled to be capable of blocking zero-sequence paths between the interconnected power distribution networks or achieving arc extinction of the single-phase earth faults; controlling dq axis components of all grid-connected ports of the flexible interconnection equipment to realize power interaction; and realizing multifunctional cooperative control by utilizing the mutual decoupling relation of the zero axis component and the dq axis component. When the interconnected power distribution network normally operates, a zero sequence path between the interconnected power distribution networks is blocked, a power interaction function is realized, and the interconnected power distribution networks are regulated and controlled; when a single-phase earth fault occurs in the interconnected power distribution network, arc extinction and power interaction of the earth fault are achieved at the same time, power full compensation is performed on downstream loads of a fault section while the fault is suppressed, if the fault does not disappear after a period of time, a line of the fault section is cut off, and power supply reliability of the downstream loads of the fault section can still be guaranteed.
Description
Technical Field
The invention relates to the technical field of safety design of a power distribution network, in particular to an integrated arc extinction method for a single-phase earth fault of an interconnected power distribution network.
Background
Complications in the operating environment of the power distribution network tend to cause single-phase ground faults. The traditional distribution networks interconnected through interconnection switches have direct electrical connection, so that the influence range of the ground fault is enlarged, and the bad degree of the fault is further worsened. The arc overvoltage generated by the arc grounding fault destroys the safe and stable operation condition of the interconnected power distribution network, and the power supply reliability of users is seriously influenced. In order to reduce the influence range of the ground fault in the interconnected power distribution network, the interconnection switch is usually directly opened so as to achieve the purpose of isolating the fault.
However, when the interconnection switch is disconnected, the power distribution network cannot be regulated, the interconnection switch can only realize on-off control, the power flowing through the interconnection switch is uncontrollable, the response speed is low due to the action process of a mechanical mechanism, the action times in the whole life cycle are limited, and large impact current exists when the interconnection switch is switched on. With the development of power electronic technology, flexible interconnection devices are proposed to replace conventional interconnection switches, providing flexible, fast, and accurate power exchange control. The flexible interconnection equipment can realize stepless differential continuous adjustment in the self capacity range, accurately control the flowing active power and reactive power, and the power electronic device has no mechanical operation mechanism, can quickly respond, has no limitation of action times, has long service life and small impact on a system.
In order to prevent the ground fault from affecting the interconnected power distribution network through the flexible interconnection equipment, a converter transformer is usually installed at a grid connection port of the flexible interconnection equipment to block a zero sequence path between the interconnected power distribution networks. However, the transformer has high cost and large volume, which is not beneficial to the popularization and application of the flexible interconnection equipment. Meanwhile, the measures only isolate the grounding fault, and actively inhibit the grounding fault. Therefore, the topological structure and the function of the flexible interconnection equipment need to be researched, and the rapid and accurate arc extinction of the single-phase earth fault of the interconnection power distribution network is realized.
Disclosure of Invention
In view of the above, the present invention aims to provide an integrated arc extinction method for a single-phase ground fault of an interconnected power distribution network, which can prevent an influence range of the ground fault from being expanded, quickly and accurately implement arc extinction of the single-phase ground fault after the single-phase ground fault occurs, implement accurate power interaction, and ensure safety of the interconnected power distribution network and power supply reliability of a load.
In order to achieve the purpose, the invention adopts the following technical scheme:
an integrated arc extinction method for single-phase earth faults of an interconnected power distribution network provides flexible interconnected equipment with fully controllable zero-axis components, and comprises the following steps:
step S1, when the interconnected power distribution network runs normally, the zero-axis component of each grid-connected port of the flexible interconnected equipment is controlled to be zero, and a zero-sequence path between the interconnected power distribution networks is blocked;
when the interconnected distribution network has a single-phase earth fault, controlling a zero-axis component of a grid-connected port at the fault distribution network side of the flexible interconnected equipment as a fault current full compensation value;
when a plurality of interconnected power distribution networks have single-phase earth faults, simultaneously controlling the zero-axis component of a grid-connected port at each fault power distribution network side of the flexible interconnection equipment to be a fault current full compensation value corresponding to each fault power distribution network side;
step S2, controlling dq axis components of each grid-connected port of the flexible interconnection equipment to realize active power and reactive power interaction between the interconnection power distribution networks;
step S3, realizing cooperative control of the zero axis component and the dq axis component of the flexible interconnection equipment by utilizing the mutual decoupling relation of the zero axis component and the dq axis component, blocking a zero sequence path between interconnection power distribution networks when the interconnection power distribution networks normally operate, realizing power interaction at the same time, and regulating and controlling the interconnection power distribution networks; when a single-phase earth fault occurs in the interconnected power distribution network, arc extinction and power interaction of the earth fault are achieved at the same time, power full compensation is carried out on downstream loads of a fault section while the earth fault is restrained, and if the fault does not disappear after a period of time, a line of the fault section is cut off.
Furthermore, the totally controllable flexible interconnection equipment of zero axis component adopts symmetrical back-to-back formula MMC as topological structure's the flexible interconnection equipment of multiport, MMC adopts half-bridge type submodule piece and the mixed cascaded form of full-bridge type submodule piece, and the port department that is incorporated into the power networks does not all connect converter transformer, and the direct current side is through series connection electric capacity midpoint ground.
Further, when the interconnected power distribution network operates normally, the zero-axis component of each grid-connected port of the flexible interconnected equipment is controlled to be zero, that is, the zero-axis current of each grid-connected port is controlled to be iZnAnd (3) blocking a zero sequence path between the interconnected power distribution networks, preventing the influence of the sudden ground fault on the interconnected power distribution networks, and realizing ground fault pre-isolation, wherein n is 1, and 2 … m is the serial number of each grid-connected port.
Further, when single-phase earth fault occurs in the interconnected distribution network, the zero-axis component of the grid-connected port of the flexible interconnected equipment fault distribution network side is controlled to be a fault current full compensation value, so that arc extinction of the single-phase earth fault of the distribution network is realized, and the method specifically comprises the following steps:
according to kirchhoff's current law, the fault current full compensation value is determined by the fault phase power supply voltage e of the fault power distribution networkXnGround parameter r of power distribution networknAnd cnIs calculated to obtain
Wherein n is the sequence number of the fault power distribution network, and X is the fault phase sequence.
Furthermore, when the plurality of power distribution networks have ground faults, the power distribution networks have fault phase power supply voltage e according to each faultXnGround parameter r of power distribution networknAnd cnCalculating respective corresponding zero-axis component reference values of the grid-connected ports, i.e.
And the variable n is the serial number of each fault power distribution network, and simultaneously, the zero-axis component of the grid-connected port of each fault power distribution network side of the flexible interconnection equipment is controlled to be a reference value which is calculated correspondingly, so that the multiple earth faults of the interconnection power distribution network are extinguished.
Further, the step S2 is to substitute the instantaneous power reference value into the dq-axis reference current calculation formula for the normal operation and the ground fault of the distribution network under the rotating coordinate system, that is
Wherein u isdnAnd uqnThe quantity p of three-phase voltage of each grid-connected port of the multi-port flexible interconnection equipment under a rotating coordinate systemnrefAnd q isnrefActive power and reactive power reference values, respectively.
Meanwhile, the sum of the interactive power between the interconnected power distribution networks is guaranteed to be zero, namely the power conservation law is met, the dq axis component of each grid-connected port of the flexible interconnection equipment is controlled to be a reference value which is calculated correspondingly, and the interaction of the active power and the reactive power between the interconnected power distribution networks is realized.
Compared with the prior art, the invention has the following beneficial effects:
1. the invention can prevent the influence range of the earth fault from being enlarged, and can quickly and accurately realize the arc extinction of the single-phase earth fault after the single-phase earth fault occurs, thereby ensuring the safe and stable operation of the interconnected power distribution network;
2. the invention can realize multifunctional cooperative control, not only can inhibit single-phase earth faults, but also can realize power interaction among interconnected power distribution networks and ensure the power supply reliability of loads.
Drawings
FIG. 1 is a topology of a multi-port flexible interconnect device in the practice of the present invention;
fig. 2 is a zero sequence equivalent circuit of the interconnected distribution network in normal operation in the implementation of the present invention;
fig. 3 is a zero sequence equivalent circuit of a single-phase earth fault of one power distribution network interconnected in the implementation of the invention;
FIG. 4 illustrates an arc suppression effect when a single-phase ground fault occurs in one of the interconnected power distribution networks in the practice of the present invention;
fig. 5 is a zero sequence equivalent circuit when single-phase earth faults occur in two interconnected power distribution networks in the implementation of the invention;
FIG. 6 illustrates an arc suppression effect when a single-phase ground fault occurs in both of two interconnected power distribution networks in an implementation of the present invention;
FIG. 7 is a graph illustrating active power and reactive power interaction waveforms between interconnected power distribution networks according to an embodiment of the present invention;
FIG. 8 shows the power interaction and single-phase earth fault arc extinction cooperative control effect of the interconnected power distribution network in the embodiment of the invention;
fig. 9 is a model structure of an interconnected 10kV distribution network in an embodiment of the present invention.
Detailed Description
The invention is further explained below with reference to the drawings and the embodiments.
Referring to fig. 1, the invention provides an integrated arc extinction method for a single-phase earth fault of an interconnected power distribution network, and provides flexible interconnected equipment with fully controllable zero-axis component, which specifically comprises the following steps:
step S1, when the interconnected power distribution network runs normally, the zero-axis component of each grid-connected port of the flexible interconnected equipment is controlled to be zero, and a zero-sequence path between the interconnected power distribution networks is blocked;
when the interconnected distribution network has a single-phase earth fault, controlling a zero-axis component of a grid-connected port at the fault distribution network side of the flexible interconnected equipment as a fault current full compensation value;
when a plurality of interconnected power distribution networks have single-phase earth faults, simultaneously controlling the zero-axis component of a grid-connected port at each fault power distribution network side of the flexible interconnection equipment to be a fault current full compensation value corresponding to each fault power distribution network side;
step S2, controlling dq axis components of each grid-connected port of the flexible interconnection equipment to realize active power and reactive power interaction between the interconnection power distribution networks;
step S3, realizing cooperative control of the zero axis component and the dq axis component of the flexible interconnection equipment by utilizing the mutual decoupling relation of the zero axis component and the dq axis component, blocking a zero sequence path between interconnection power distribution networks when the interconnection power distribution networks normally operate, realizing power interaction at the same time, and regulating and controlling the interconnection power distribution networks; when a single-phase earth fault occurs in the interconnected power distribution network, arc extinction and power interaction of the earth fault are achieved at the same time, power full compensation is carried out on downstream loads of a fault section while the earth fault is restrained, and if the fault does not disappear after a period of time, a line of the fault section is cut off.
In this embodiment, zero-axis components of each grid-connected port of the flexible interconnection equipment are controlled to block a zero-sequence path between the interconnection power distribution networks or realize single-phase earth fault arc extinction; controlling dq axis components of each grid-connected port of the flexible interconnection equipment to realize active power and reactive power interaction between the interconnection power distribution networks; and realizing cooperative control of the zero-axis component and the dq-axis component by utilizing the mutual decoupling relation of the zero-axis component and the dq-axis component. When the interconnected power distribution network normally operates, blocking a zero sequence path between the interconnected power distribution networks, simultaneously realizing a power interaction function, and regulating and controlling the interconnected power distribution network; when a single-phase earth fault occurs in the interconnected power distribution network, arc extinction and power interaction of the earth fault are achieved at the same time, power full compensation is performed on downstream loads of a fault section while the fault is suppressed, if the fault does not disappear after a period of time, a line of the fault section is cut off, and power supply reliability of the downstream loads of the fault section can still be guaranteed. When a plurality of flexibly interconnected power distribution networks have single-phase earth faults, the zero-axis component of the grid-connected port of each fault power distribution network side of the flexible interconnection equipment is controlled simultaneously, and multiple earth faults arc extinction of the interconnected power distribution networks is realized
In this embodiment, the flexible interconnection device with completely controllable zero-axis component adopts a multi-port flexible interconnection device with a topology structure of a symmetric "back-to-back" MMC, as shown in fig. 1, the MMC adopts a mixed cascade form of a half-bridge sub-module and a full-bridge sub-module, a grid-connected port is not connected with a converter transformer, and a direct current side is grounded through a midpoint of a series capacitor, thereby creating a completely controllable zero-sequence path.
In this embodiment, as shown in fig. 2, for a zero-sequence equivalent circuit during normal operation of a power distribution network interconnected by a dual-port flexible interconnection device, zero-axis components of two grid-connected ports of the flexible interconnection device are both controlled to be zero, that is, zero-axis current of each grid-connected port is controlled to be iZ1＝iZ2And (5) blocking a zero sequence path between the interconnected power distribution networks to prevent the influence of the sudden ground fault on the interconnected power distribution networks and realize ground fault pre-isolation. Similarly, a multi-port flexible interconnect deviceControlling the zero axis current of each grid-connected port to be iZnWhere n is 1, and 2 … m is the serial number of each grid connection port.
In this embodiment, as shown in fig. 3, the zero-axis component of the grid-connected port on the side of the power distribution network with the fault of the flexible interconnection device is controlled to be a fault current full compensation value for a zero-sequence equivalent circuit when a single-phase ground fault occurs in one of the power distribution networks interconnected by the dual-port flexible interconnection device. According to kirchhoff's current law, the fault current full compensation value is determined by the fault phase power supply voltage e of the fault power distribution networkC2Ground parameter r of power distribution network2And c2Is calculated to obtain
And realizing the arc extinction of the single-phase earth fault of the power distribution network, as shown in figure 4. The zero-axis component of the grid-connected port at the side of the non-fault power distribution network is kept to be zero, i Z10. Similarly, when one power distribution network interconnected by the multi-port flexible interconnection equipment has single-phase earth fault, the zero-axis component of the grid-connected port on the side of the power distribution network with the fault of the flexible interconnection equipment is controlled to be
Wherein n is the sequence number of the fault power distribution network, and X is the fault phase sequence. And the zero-axis component of the grid-connected ports on the other non-fault power distribution network sides is kept to be zero.
In this embodiment, as shown in fig. 5, the zero sequence equivalent circuit is obtained when a single-phase ground fault occurs in two power distribution networks interconnected by a dual-port flexible interconnection device. From the fault phase supply voltage e of two faulty distribution networksC1、eC2Ground parameter r of power distribution network1、r2And c1、c2Calculating the zero axis component reference values corresponding to the grid-connected ports respectively, and controlling the zero axis components of the grid-connected ports on two fault power distribution network sides of the flexible interconnection equipment to be respectively
And
and realizing the arc extinction of the double earth faults of the interconnected distribution network as shown in figure 6. Similarly, when a plurality of power distribution networks interconnected by the multi-port flexible interconnection equipment have ground faults, the power distribution networks have fault phase power supply voltage e according to each faultXnGround parameter r of power distribution networknAnd cnCalculating respective zero-axis component reference values corresponding to the grid-connected ports, i.e.
Wherein, the variable n is the serial number of each fault distribution network. And the multiple earth fault arc extinction of the interconnected power distribution network is realized by simultaneously controlling the zero-axis component of the grid-connected port of each fault power distribution network side of the multi-port flexible interconnected equipment. And the zero-axis component of the grid-connected ports on the other non-fault power distribution network sides is kept to be zero.
In this embodiment, step S2 specifically includes: under a rotating coordinate system, substituting the instantaneous power reference value into a dq-axis reference current general calculation formula when the power distribution network is in normal operation and has a ground fault, namely
The formula is obtained by simultaneous instantaneous power theory formula. Wherein u isdnAnd uqnThe quantity p of three-phase voltage of each grid-connected port of the multi-port flexible interconnection equipment under a rotating coordinate systemnrefAnd q isnrefActive power and reactive power reference values, respectively.
Meanwhile, the sum of the interactive power among the interconnected power distribution networks is guaranteed to be zero, namely the power conservation law is met. Active power and reactive power interaction between interconnected power distribution networks is realized by controlling dq axis components of each grid-connected port of the flexible interconnection equipment to be reference values which are respectively and correspondingly calculated, as shown in fig. 7.
In this embodiment, step S3 specifically includes:
according to the mutual decoupling relation of the zero-axis component and the dq-axis component, the zero-axis component control and the dq-axis component control of the flexible interconnection equipment are mutually independent, and multifunctional cooperative control can be achieved. When the interconnected power distribution network normally operates, zero-axis components are controlled to block zero-sequence paths between the interconnected power distribution network, sudden ground faults are prevented from affecting the interconnected power distribution network, ground fault pre-isolation is achieved, dq-axis components are controlled to achieve power interaction, and the interconnected power distribution network is regulated and controlled. When a single-phase earth fault occurs in the interconnected power distribution network, the zero-axis component is controlled to actively suppress the earth fault, the dq-axis component is controlled to realize power interaction, power full compensation is carried out on downstream loads in a fault section, if the fault does not disappear after a period of time, a line in the fault section is cut off, and the power supply reliability of the downstream loads in the fault section can still be guaranteed
According to the mutual decoupling relation of the zero-axis component and the dq-axis component, the zero-axis component control and the dq-axis component control of the flexible interconnection equipment are mutually independent, and multifunctional cooperative control can be achieved. As shown in fig. 8, the effect of cooperative control of power interaction and ground fault arc extinction of the power distribution networks interconnected by the dual-port flexible interconnection device is achieved, when the interconnection power distribution network operates normally, a zero-axis component is controlled to block a zero-sequence path between the interconnection power distribution networks, so that an abrupt ground fault is prevented from affecting the interconnection power distribution network, and ground fault pre-isolation is achieved; meanwhile, the dq axis component is controlled to realize power interaction, and the interconnected power distribution network is regulated and controlled. When a single-phase earth fault occurs in the interconnected power distribution network, controlling a zero-axis component to actively suppress the earth fault; and meanwhile, the dq axis component is controlled to realize power interaction, power full compensation is carried out on the downstream load of the fault section, if the fault does not disappear after a period of time, the line of the fault section is cut off, and the power supply reliability of the downstream load of the fault section can still be guaranteed. The implementation method of power interaction and single-phase earth fault arc extinction cooperative control of the power distribution network interconnected by the multi-port flexible interconnection equipment is the same.
Particularly, for verifying the effectiveness of the single-phase earth fault integrated arc extinction method for the interconnected power distribution network, MATLAB/SIMULINK software is used for respectively building a 10kV power distribution network simulation model interconnected by double-port and multi-port flexible interconnection equipment. The 10kV power distribution network model structure interconnected by the dual-port flexible interconnection equipment is shown in FIG. 9. Simulation results of the two models show that the method can prevent the influence range of the earth fault from being enlarged, and can quickly and accurately realize arc extinction of the single-phase earth fault after the single-phase earth fault occurs, so that safe and stable operation of the interconnected power distribution network is guaranteed. Meanwhile, the multifunctional cooperative control can inhibit the ground fault, realize the power interaction between the interconnected power distribution networks and guarantee the power supply reliability of the load.
The above description is only a preferred embodiment of the present invention, and all equivalent changes and modifications made in accordance with the claims of the present invention should be covered by the present invention.
Claims (6)
1. The integrated arc extinction method for the single-phase earth fault of the interconnected power distribution network is characterized by providing flexible interconnected equipment with completely controllable zero-axis component, and comprising the following steps of:
step S1, when the interconnected power distribution network runs normally, the zero-axis component of each grid-connected port of the flexible interconnected equipment is controlled to be zero, and a zero-sequence path between the interconnected power distribution networks is blocked;
when the interconnected distribution network has a single-phase earth fault, controlling a zero-axis component of a grid-connected port at the fault distribution network side of the flexible interconnected equipment as a fault current full compensation value;
when a plurality of interconnected power distribution networks have single-phase earth faults, simultaneously controlling the zero-axis component of a grid-connected port at each fault power distribution network side of the flexible interconnection equipment to be a fault current full compensation value corresponding to each fault power distribution network side;
step S2, controlling dq axis components of each grid-connected port of the flexible interconnection equipment to realize active power and reactive power interaction between the interconnection power distribution networks;
step S3, realizing cooperative control of the zero axis component and the dq axis component of the flexible interconnection equipment by utilizing the mutual decoupling relation of the zero axis component and the dq axis component, blocking a zero sequence path between interconnection power distribution networks when the interconnection power distribution networks normally operate, realizing power interaction at the same time, and regulating and controlling the interconnection power distribution networks; when a single-phase earth fault occurs in the interconnected power distribution network, arc extinction and power interaction of the earth fault are achieved at the same time, power full compensation is carried out on downstream loads of a fault section while the earth fault is restrained, and if the fault does not disappear after a period of time, a line of the fault section is cut off.
2. The single-phase ground fault integrated arc extinction method for the interconnected power distribution network according to claim 1, wherein the flexible interconnection device with the fully controllable zero-axis component adopts a multi-port flexible interconnection device with a topological structure of symmetrical back-to-back type MMC, the MMC adopts a mixed cascading mode of a half-bridge type submodule and a full-bridge type submodule, a converter transformer is not connected to a grid-connected port, and a direct current side is grounded through a middle point of a series capacitor.
3. The single-phase ground fault integrated arc extinction method for the interconnected power distribution network according to claim 2, wherein when the interconnected power distribution network operates normally, the zero-axis component of each grid-connected port of the flexible interconnected equipment is controlled to be zero, namely the zero-axis current of each grid-connected port is controlled to be iZnAnd (3) blocking a zero sequence path between the interconnected power distribution networks, preventing the influence of the sudden ground fault on the interconnected power distribution networks, and realizing ground fault pre-isolation, wherein n is 1, and 2 … m is the serial number of each grid-connected port.
4. The single-phase earth fault integrated arc extinction method of the interconnected power distribution network according to claim 2, characterized in that when the interconnected power distribution network has a single-phase earth fault, a grid-connected port zero-axis component of a fault power distribution network side of the flexible interconnected equipment is controlled to be a fault current full compensation value, so that arc extinction of the single-phase earth fault of the power distribution network is realized, and the method specifically comprises the following steps:
according to kirchhoff's current law, the fault current full compensation value is determined by the fault phase power supply voltage e of the fault power distribution networkXnGround parameter r of power distribution networknAnd cnIs calculated to obtain
Wherein n is the sequence number of the fault power distribution network, and X is the fault phase sequence.
5. Single-phase earth fault integration of interconnected distribution network according to claim 2The arc extinction method is characterized in that when a plurality of power distribution networks have ground faults, the power distribution networks are subjected to power supply voltage e according to the fault phase of each faultXnGround parameter r of power distribution networknAnd cnCalculating respective corresponding zero-axis component reference values of the grid-connected ports, i.e.
And the variable n is the serial number of each fault power distribution network, and simultaneously, the zero-axis component of the grid-connected port of each fault power distribution network side of the flexible interconnection equipment is controlled to be a reference value which is calculated correspondingly, so that the multiple earth faults of the interconnection power distribution network are extinguished.
6. The method for integrally extinguishing the single-phase earth fault of the interconnected distribution network according to claim 1, wherein the step S2 is implemented by substituting the instantaneous power reference value into a dq-axis reference current calculation formula during normal operation and earth fault of the distribution network under a rotating coordinate system, namely
Wherein u isdnAnd uqnThe quantity p of three-phase voltage of each grid-connected port of the multi-port flexible interconnection equipment under a rotating coordinate systemnrefAnd q isnrefActive power and reactive power reference values, respectively.
Meanwhile, the sum of the interactive power between the interconnected power distribution networks is guaranteed to be zero, namely the power conservation law is met, the dq axis component of each grid-connected port of the flexible interconnection equipment is controlled to be a reference value which is calculated correspondingly, and the interaction of the active power and the reactive power between the interconnected power distribution networks is realized.
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| 郭谋发;游建章;林先辉;杨耿杰;缪希仁;: "适应线路参数及负载变化的配电网柔性优化消弧方法", 电力系统自动化, no. 08 * |
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| Publication number | Publication date |
|---|---|
| CN114221320B (en) | 2023-11-10 |
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